Isometric muscular exercise causes increases in heart rate, blood pressure, and ventilation. At least part of this response appears to be reflexly evoked by neural input from the exercising muscle. This reflex may be conveniently studied in acute animal models utilizing stimulation of cut ventral roots to achieve muscle contraction which in turn evokes the cardiovascular response. The proposed research will investigate the role of the brainstem cardiovascular centers in the generation of this pressor response. This research will be conducted by: (1) examining the effects of systematically lesioning the rostral neuraxis and specific nuclei in the brainstem with demonstrated pressor function (i.e., following the lesions are the animals capable of generating an isometric exercise pressor response?) These nuclei include lateral reticular nucleus, nucleus parvocellularis, paramedian reticular nucleus, and the rostral raphe nuclei. (2) Microelectrode recording from these nuclei and spinal interneurons. The cells in these areas can be characterized as to their afferent input, especially with regard to the high threshold nuscle afferents associated with the pressor response as well as monitored during the generation of the pressor response itself. (3) Anatomical experiments with horseradish peroxidase labelling which will establish what additional spinal and supraspinal structures may be providing modulating input for the exercise response. The results of these experiments will establish the components of the central nervous system (CNS) which are responsible for the refle cardiovascular adaptation to isometric muscular exercise and the manner in which they respond. In addition, the results are generalizable in that they provide a valuable example of how the CNS responds in making cardiovascular adjustments as a whole.